1. Field of the Invention
The present invention relates to a display device, and more particularly to a scanning display device for performing a scanning action using a scan mirror.
2. Discussion of the Related Art
A conventional laser scanning display device uses a polygon mirror and a galvanometer to scan a laser beam acting as a light signal on the screen. In this case, the polygon mirror may scan the laser beam in a horizontal direction, and the galvanometer may scan the laser beam in a vertical direction. Otherwise, the polygon mirror may scan the laser beam in the vertical direction, and the galvanometer may scan the laser beam in the horizontal direction.
However, considering system minimization, resolution, reliability, and production costs, a large number of research institutions generally use a MEMS mirror instead of a polygon mirror. For the convenience of description, the above-mentioned MEMS mirror is referred to as a micro-scanning mirror.
The micro-scanning mirror is activated at a resonance frequency based on spring-damper characteristics of a hinge during the horizontal scanning process. If the micro-scanning mirror is driven at the resonance frequency, a plurality of scanning angles can be implemented with less energy. In this case, the resonance frequency is designed to be equal to a horizontal synchronous frequency of the screen. Also, the micro-scanning mirror may scan the laser beam on the screen in the vertical direction.
The micro-scanning mirror driven at a resonance frequency to scan the laser beam in the horizontal direction scans the laser beam on the screen in the form of a sinusoid. Therefore, the micro-scanning mirror has different speeds at individual scanning locations, such that the laser-beam traveling time per unit length is changed. Therefore, there is a difference in quantity of the laser beam at individual pixels of the screen, and there is a difference in brightness at individual pixels of the screen.
FIGS. 1A and 1B are conceptual diagrams illustrating a difference in brightness of the scanned screen of the conventional display device. FIG. 1A shows the distribution of brightness of the screen. FIG. 1B is a graph illustrating a difference in brightness of the screen, in which the horizontal axis of the graph indicates the location and the vertical axis of the graph indicates the brightness.
In more detail, the brightness difference occurs according to the screen locations shown in FIG. 1A, as denoted by FIG. 1B. In other words, as shown in FIG. 1B, the closer the brightness is to the center of the screen, the darker the brightness. The closer the brightness is to the edge of the screen, the lighter the brightness.
FIGS. 2A to 2C are conceptual diagrams illustrating correction of the brightness difference shown in FIG. 1B. In more detail, FIG. 2A shows the distribution of the screen brightness. FIG. 2B is a graph illustrating a light-quantity drive signal. FIG. 2C is a graph of the correction result.
In order to correct the brightness difference shown in FIG. 1B, the level of the laser drive signal is adjusted as shown in FIG. 2B. In the case of adjusting the drive-signal level, the brightness difference 10 between the screen center and the screen edge may be adjusted to be uniform as shown in FIG. 2C.
However, the screen display device is driven at a low brightness of the laser beam, such that overall brightness may unavoidably deteriorate. The laser-beam brightness shown in FIG. 2B must be adjusted according to locations, such that an additional signal processing control is required to adjust the laser-beam brightness.
FIG. 3 shows the screen distortion depending upon the scanning speed.
In this case, when the laser beam scanned by the micro-scanning mirror moves on the screen, the moving speed measured at the center of the screen is difference from another moving speed measured at the edge of the screen. Therefore, if the image is transmitted at the same speed during the horizontal scanning operation, the distorted screen image shown in FIG. 3 may occur.